The invention relates to straight chain perfluoroolefins of medium chain length with terminal or internal double bonds which are valuable as highly reactive intermediate products in the production of surface active agents.
Among the straight chain perfluorinated olefins those are known which have a chain length increasing up to C.sub.9. These short chain perfluoroolefins have been widely investigated regarding their properties. However, there is a scarcity of data regarding the chemical properties of the homologs with a carbon chain of C.sub.7 to C.sub.9 because of the difficulties in producing these compounds. The short chain perfluorinated olefins can easily be polymerized. They can also be converted to oligomers ionically, or can be reacted by means of nucleophilic reaction. They are mainly used as starting products for making fluoropolymers and constitute intermediate products, for instance in the production of fire extinguishing agents and of propellant gases.
There have also already been prepared highly branched perfluoroolefins such as the perfluoro-4-ethyl-3,4-dimethyl-hex-cis-2-ene which latter have a chain length of 6 to 7 carbon atoms and are highly reactive to nucleophilic reaction components because of their branched structure and the resulting negative induction effect. They are used as starting products or intermediate products for making surface active agents.
It is also known that perfluoroolefins can be obtained by thermal decomposition of dry alkali salts of perfluorinated alkyl carboxylic acids [J. D. La Zerte, L. J. Hals, T. S. Reid, G. H. Smith, Journal American Chemical Society 75 (1953) 4525]. This method is, however, not suitable for large scale operations for economic reasons.
A further process for obtaining perfluoroolefins is the ionic conversion to oligomers of tetrafluoroethylene (British Pat. No. 1,082,127) in which case highly branched perfluorinated olefins such as the perfluoro-4-ethyl-3,4-dimethyl-hex-cis-2-ene are formed.
These reactions are carried out on an industrial scale in batch operations in a steel autoclave under exclusion of oxygen and humidity in an anhydrous organic solvent in the presence of the very expensive cesium fluoride. The formed perfluorinated oligomerolefin C.sub.10 F.sub.20 is obtained after separating off the byproducts formed by distillation in yields of between 50 and 60%. This process requires the observation of specific safety procedures in order to avoid an undesirable spontaneous exothermic polymerization when working under pressure with the tetrafluoroethylene.
It has also become known from German Patent Nos. 112,589 and 112,197 that highly fluorinated polymers can be degraded by chemical radiation methods. The thusly formed mixture of various degradation products is not defined further chemically. A disadvantage is that the degradation products must be removed from the reaction zone by means of a carrier gas followed by isolation thereof from the carrier gas by fractionation techniques in order to obtain their separation. The carrier gas stream hereby also entrains the insufficiently degraded polymers as a fine dust. Further complete isolation of the degradation products, because of the high steam pressures, is possible only by application of expensive adsorption batteries or low temperatures.
It is therefore an object of the present invention to form straight chain perfluoroolefins of medium chain lengths which are distinguished structurally and by their composition from the prior art perfluoroolefins and which can be used as intermediate or starting products for making surface active agents.